What is a concrete Retarder?
Concrete retarders are the mixture that slows down the chemical process of hydration so that the concrete remains plastic and workable for a long time. Retarders are used to overcome the accelerating effect of high temperature on establishing the properties of concrete in hot climates.
Requirements and purposes of Concrete Retarder
1. It increases the setting time of concrete.
2. It improves the workability of concrete.
3. The appearance of the concrete is greatly improved.
4. Drying shrinkage and creep rate are also increased.
Types of Retarder in Concrete
Retarders are divided into two categories depending on the nature of the retarders.
- Organic Retarder
- Inorganic Retarder or Chemical retarder
A) Organic Retarder
1. Lignosulphonates
2. Phosphonates
3. Sugars, etc
B) Inorganic Retarder
1. Phosphonates
2. Borates
3. salts of pb,zn,cu,As,sb,etc
Effects of Retarder on Concrete
1. Strength
2. Practicality and rational values
3. Slump loss
4. Air entrainment
5. Freeze-thaw cycle
6. Bleeding
7. Heat of hydration
8. Volume distortion
9. Durability
Advantages of Retarder in Concrete
1. Retarders extend the setting time of the concrete and maintain the functionality and consistency for an extended period of time.
2. In a large construction project, a concrete retarder prevents the formation of cold joints in gradual lift and makes the concrete workable.
3. Using retarders, we can compensate for the accelerated impact of high temperatures towards the initial setting time and reduces the risks of long-distance delivery in hot weather.
4. Concrete retarders reduce isolation and bleeding in poor sand grinding is unavoidable.
Disadvantage of retarder in concrete
1. Concrete retarders may be used with water to avoid cracks and bleeding.
2. Depending on it water-cement ratio, cement content, and the amount of C3a in the cement, the dose of retarder admixture should be within the limit.
3. Concrete retarders can undergo variable action on different types of cement when used in varying quantities.
Uses of Concrete Retarder
1. Most commonly used in concrete in the summer season.
2. The retarders sprayed on the surface of the formwork, preventing the hardening of the matrix at the interface of the concrete and formwork while hardening the rest of the concrete.
3. Retarders are used for large-scale construction work and gritting oil wells.
4. It is often used in concrete have to be placed in difficult conditions, delays in transporting and placing.
5. It is also used for pouring consolidation castings without the formation of cold joints, also used in grouting oil wells.
Hence, Concrete retarders delayed the hydration of cement, a large number of pours and castings are consolidated without forming cold joints.
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